In studies in which tissue concentrations of cholesterol and total lipids were determined in male and female rats fed a control diet containing fat, the effects of gonadectomy were much smaller than in animals fed a fat-free diet in which gonadectomy tended to reverse the sex differences observed in these lipid values. Other phases of lipid metabolism were shown to be sex-linked as well. Gonadectomy resulted in decreased synthesis of cholesterol in rat liver slices and changes in the fatty acid composition of cholesterol esters in the liver.